For those wondering, Hirari has a number of volumes whose numbers she has skipped. These aren't "hidden" or "exclusive" volumes of the Hilari Bomber Laboratory series, she simply misnumbered them and never went back to fix them. (Anybody who watches her volumes will recognize that she has a bad habit of accidentally misnumbering each episode of her series). Those skipped include Volumes: 52, 62, 65, 72, 73, and 75.
Once again, these aren't any hidden or lost volumes... they DO NOT EXIST.
Also, the current and most recent volume number as of September 2024 is Volume 79, released back in March of 2024.
Hope this helps fellow collectors out there!